Business, science and entertainment applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical and convenient means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved magnetic read/write heads, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 512 or more data tracks.
To record data on a magnetic medium such as a magnetic tape or a disk, a write transducer traditionally generates a magnetic flux that sets magnetic transitions in the medium in a manner corresponding to binary data. Conventional writers have electrically conducting coils that wrap around a yoke in one or more planes. This design is sometimes referred to as a “pancake” configuration. The yoke transports the flux generated by the coil to a pole tip, which has a non-magnetic gap where the flux forms a field that fringes into the medium.
The coils are generally plated copper, which is a good conductor. However, since many windings may be needed for generating the flux necessary to overcome the coercive force of the media at a reasonable current the width of the writer can be very large. Thus, pancake configurations are often made with two layers of coils, but even these can be very wide. This large width, however, limits how closely writers may be spaced in an array, such as on a multitrack tape head. The more wraps in a single-plane coil, the wider the overall writer is, potentially making spacing an issue. Stacking coil layers is possible, but the plated coils themselves are relatively thick and require complex insulation processing. The resultant transducers are relatively tall, and the extra height can degrade magnetic performance by lengthening the yoke and constricting flux (saturation).
When a tape is written, the span of data just written is the span of the head elements. However, expansion and contraction of the tape prior to reading results in misregistration between the altered tape and the head. Present tapes typically expand and contract by approximately 1 part in 1000, or 0.1%.
In current Linear Tape Open (LTO) systems, the heads include servo readers that are approximately 2.9 mm apart. The tape media also includes servo tracks having a spacing of approximately 2.9 mm, thereby defining data bands of approximately 2.9 mm wide. A 0.1% expansion over 2.9 mm results in 2.9 micrometers of expansion. Accordingly, the data tracks themselves must be greater than the reader widths plus 2.9 micrometers or the readback will suffer from expansion- or contraction-induced misregistration. This may be reduced somewhat by shingling tracks according to how much the tape is dilated or contracted at the time of writing. However, this requires prior knowledge of exact servo reading positions and other knowledge. Accordingly, present tape formats are reaching their limits as far as increasing track density is concerned. To illustrate, consider the following example.
Assume tracks are not shingled, as may be the case for some products. Then, read sensor width is chosen to be about ½ the track width on the tape. Assume that the tracks are 6 micrometers wide. The sensor is then 3 microns wide. If at the outer tracks, there is 3 micrometers of tape expansion misregistration, the readers over the outer data bands will be riding along the edge of the data track. Then the reader may go off the track due to uncompensated lateral tape excursions. Accordingly, the track widths (in this example) cannot be made smaller without increased risk of misreads due to tape lateral transients.
One method for compensating for tape lateral expansion and contraction is statically rotating the head and then making small angular adjustments to keep the readers/writers in the head aligned to tracks on the tape. However, the static rotation leads to skew-related misregistration and is generally complex and difficult to implement. For example tilted heads must be constructed so as not to steer tape, etc.
Another proposed solution attempts to control the tape width by controlling tape tension. However, this method works over a limited range only, and generally does not provide enough control.
What is therefore needed is a magnetic write transducer that is very compact in comparison to traditional pancake type writers. Such a write transducer would enable such things as creation of a multi-transducer head an element array having a shorter span, which in tarn alleviates many of the detrimental effects of tape lateral expansion and contraction.